Atheism and Anarchism: ideological cousins?

Some people believe that there is a strong connection between atheism and Anarchism, others believe there is no such connection. Certainly it is true that Anarchist thinkers have been strongly unsympathetic to organized religion and tend to be atheists, but the reverse has not been true. Why is that? And what is the connection?

Anarchism is a position about society and undesirable structures within it (that is to say, the belief that hierarchies are unjustified). Atheism, on the other hand, is an ontological position (about the existence of gods). But if you ask atheists why they see the need to label themselves and discuss atheism, they will almost invariably answer you that Christian dogma infiltrating itself in the schools and politics is the main issue. Therefore atheism does reduce itself to a social issue to some extent.